Machine type communication (MTC) that is also referred to as machine-to-machine (M2M) communication, or the Internet of Things (IoT) will be an important application in a future communications field. One type of important MTC system is a communications system based on an existing cellular network infrastructure. This type of MTC communications system is usually referred to as cellular MTC or a cellular IoT (CIoT).
In a CIoT system, a base station may perform downlink scheduling or uplink scheduling on a user equipment (UE). An example in which a base station performs uplink scheduling on UE is used. A process in which the base station performs uplink scheduling on the UE includes: The UE sends uplink data on a time-frequency resource indicated by the base station; after receiving the uplink data, the base station sends acknowledgement/negative acknowledgement (ACK/NACK) information to the UE according to a status of correctly or incorrectly receiving the data; and after the UE receives the ACK/NACK information, if the ACK/NACK information is an ACK, this data transmission is correctly completed; or if the ACK/NACK information is a NACK, it represents that the base station fails to correctly receive the data, and the UE needs to wait for the base station to schedule the UE again to resend the data.
In the process in which the base station performs uplink scheduling on the UE, the base station may schedule, by using a bitmap indication, the UE to receive the ACK/NACK information sent for the uplink data. The bitmap indication means that the base station respectively indicates ACK/NACK information of multiple UEs by using multiple pieces of bit information. Because each bit in a bitmap has no special meaning, the base station needs to specify a correspondence between each UE and each bit in the bitmap, that is, specify that a specific bit in the bitmap indicates a status of receiving uplink data of which UE.
In the prior art, a base station may specify a correspondence between each UE and each bit in a bitmap by using an implicit mapping method. Specifically, the implicit mapping method is to preset a rule for calculating a location relationship between the base station and the UE. The UE obtains, by means of calculation according to the calculation rule and known prior information, a bit corresponding to the UE in the bitmap.
However, for example, as shown in FIG. 1, a base station schedules, by using a scheduling block in a physical downlink control channel (PDCCH), UE to transmit uplink data. A scheduling block for UE a is a PDCCH1, and a scheduling block for UE b is a PDCCH2. The UE a has more uplink data, is scheduled to perform uplink transmission for a longer time, and needs to receive, in a bitmap x, ACK/NACK information sent by the base station for the UE a. The UE b has less uplink data, is scheduled to perform uplink transmission for a shorter time, and also needs to receive, in the bitmap x, ACK/NACK information sent by the base station for the UE b. Therefore, it can be learned that the UE a and the UE b may be mapped to a same bit in the bitmap x by using the implicit mapping method, thereby resulting in a problem that bits of different UEs are in collision.